Which of the following elements are considered in acoustical systems?

The elements that are considered in acoustical systems focus on controlling sound and improving the auditory environment within a space. Noise reduction is crucial as it minimizes unwanted sound, creating a more peaceful atmosphere, particularly in environments like offices, recording studios, or public spaces. Sound transmission pertains to how sound travels between different areas, which is vital for maintaining privacy and reducing distractions.

The ceiling attenuation class (CAC) is particularly relevant in evaluating how well a ceiling can reduce sound transmission between rooms. This metric helps designers select appropriate materials and designs for ceilings to enhance acoustic performance. Sound masking refers to the introduction of background noise to help cover up distracting sounds, further contributing to a comfortable auditory setting.

Therefore, this set of options directly addresses the main concerns and objectives of acoustical design, making it the accurate answer in the context of the question. The other options either pertain to different aspects of building design such as thermal properties, lighting, or aesthetic considerations, which do not directly relate to acoustics.